MM-13207 Add customizable timeout for link metadata and improve caching of errors (#10188)

* MM-13207 Add customizable timeout for link metadata and improve caching of errors

* Rename LinkMetadataTimeout to LinkMetadataTimeoutMilliseconds

* Add diagnostics for LinkMetadataTimeoutMilliseconds

model/config.go

@@ -139,6 +139,8 @@ const (
 	NATIVEAPP_SETTINGS_DEFAULT_ANDROID_APP_DOWNLOAD_LINK = "https://about.mattermost.com/mattermost-android-app/"
 	NATIVEAPP_SETTINGS_DEFAULT_IOS_APP_DOWNLOAD_LINK     = "https://about.mattermost.com/mattermost-ios-app/"
 
+	EXPERIMENTAL_SETTINGS_DEFAULT_LINK_METADATA_TIMEOUT_MILLISECONDS = 5000
+
 	ANALYTICS_SETTINGS_DEFAULT_MAX_USERS_FOR_STATISTICS = 2500
 
 	ANNOUNCEMENT_SETTINGS_DEFAULT_BANNER_COLOR      = "#f2a93b"
@@ -692,9 +694,10 @@ func (s *MetricsSettings) SetDefaults() {
 }
 
 type ExperimentalSettings struct {
-	ClientSideCertEnable *bool
-	ClientSideCertCheck  *string
-	EnablePostMetadata   *bool
+	ClientSideCertEnable            *bool
+	ClientSideCertCheck             *string
+	EnablePostMetadata              *bool
+	LinkMetadataTimeoutMilliseconds *int64
 }
 
 func (s *ExperimentalSettings) SetDefaults() {
@@ -709,6 +712,10 @@ func (s *ExperimentalSettings) SetDefaults() {
 	if s.EnablePostMetadata == nil {
 		s.EnablePostMetadata = NewBool(false)
 	}
+
+	if s.LinkMetadataTimeoutMilliseconds == nil {
+		s.LinkMetadataTimeoutMilliseconds = NewInt64(EXPERIMENTAL_SETTINGS_DEFAULT_LINK_METADATA_TIMEOUT_MILLISECONDS)
+	}
 }
 
 type AnalyticsSettings struct {